A common means for modifying the lift characteristics of an aircraft wing for lower speed operation is to use leading and/or trailing edge devices which either pivot or slide outwardly from the leading or trailing edge of the aircraft wing to a deployed position. The contours of these movable airfoils are determined largely by the shape of the wing of which the movable airfoil is a part. In the case where the movable airfoil is a leading edge slat attached to a wing utilized in high speed aircraft, the contour of the slat is relatively flat with a small radius of curvature about the nose making the slat subject to early airflow separation as the angle of attack of the airflow relative to the slat is increased. This airflow separation may be eliminated by increasing the camber of the leading edge slat upper surface thereby preventing airflow separation as the slat is deployed tohigher angle of attack positions.
An apparatus for varying the camber of a movable slat was described in U.S. Pat. No. 3,272,458 by Bracka wherein a variable camber leading edge device, having a movable nose portion which is rotated when the device is extended, imparts to the upper surface of the device a curved configuration. A first track slidably mounted to the wing drives the device between the extended and retracted positions, and a second camming track, together with linkage means, rotates the leading edge device to achieve the desired cambered surface.
It is difficult to achieve an aerodynamically desirable cambering program throughout the extension and retraction of a separate flap or slat which moves relative to the fixed portion of a wing because of the large number of interconnected linkage members that must be moved to produce a precisely coordinated movement while overcoming the interference, containment and load problems associated with such a mechanism. Precision is necessary in order to achieve pure bending of the airfoil surfaces rather than a buckling effect which results in uneven airfoil surfaces which are disruptive to the flow of air across the airfoil, and to avoid the imposition of large compression loads on the flexible skin portion which can result in fatigue, damage and failure over extended periods of time.
A number of apparatus also have been disclosed for varying the camber of a wing. For example, in U.S. Pat. No. 4,475,702 by Cole, there is disclosed a variable camber leading edge wing device having a movable nose section which is attached to an upper flexible panel extending rearwardly from the nose section, and which is moved by a rotary pinion gear engaged to an arcuate cam track.
U.S. Pat. No. 4,427,168--McKinney, disclosed a variable camber leading edge wing device having a movable nose section which is attached to an upper flexible panel extending rearwardly from the nose section. The nose section is moved by a rotary driven 4-bar linkage having a support link which is interconnected to the 4-bar linkage and to the upper flexible panel at a midpoint thereof to maintain the flexible skin in a controlled constant curvature when the nose section is moved.
Statkus, U.S. Pat. No. 4,351,502 disclosed a variable camber leading/trailing edge wing device having a movable nose section attached to an upper flexible panel extending rearwardly from the nose section. The nose section is moved by two sets of 4-bar linkages, one set of which controls horizontal and vertical displacement of the nose section, and the other set of which controls both the angle of rotation of the nose section as well as the moment applied to the chordwise midpoint of the flexible upper panel to maintain constant controlled curvature of the flexible panel.
In Rowarth, U.S. Pat. No. 4,200,253 a variable camber leading edge wing device is disclosed which is pivotally mounted to a wing at a single pivot point. The wing device includes a flexible upper skin surface which is maintained in a desired curved profile by a pair of double piano hinge link assemblies attached to the flexible upper skin, and to a rearwardly extending portion of the wing leading edge which terminates at the single pivot point.
In U.S. Pat. No. 4,171,787 by Zapel, there is disclosed a variable camber leading edge of an airfoil having a movable nose section attached to rearwardly extending upper and lower flexible panels, and which is moved between extended and retracted positions by a mounting arm attached to a lower portion of the nose section to swing the nose section downwardly and rearwardly. A toggle linkage connected to an upper portion of the nose section shortens the chordal length of the arc of the upper flexible skin to maintain a continuous cambered curve.
In U.S. Pat. No. 4,159,089--Cole, there is disclosed a variable camber leading edge flap which is movable between a retracted position where it is stowed in a bottom underside portion of the wing, and an extended position downwardly and forwardly from the leading edge of the wing where a flexible upper surface of the flap is flexed to define a curved cambered surface.
Zapel, U.S. Pat. No. 4,131,253 disclosed a variable camber wing trailing edge having upper and lower flexible skin surfaces, and having a walking beam which is movable forwardly or rearwardly to cause a locating arm pivotally connected to the beam to pivot downwardly or upwardly causing corresponding movement of the trailing edge section which flexes the upper and lower skinned surfaces to generate a cambered wing trailing edge.
In McKinney, U.S. Pat. No. 4,040,579 there is disclosed a variable camber leading edge airfoil having a nose section attached to an upper flexible skin surface extending rearwardly from the nose section and also having a lower rigid panel pivotally connected to a lower portion of the nose section and to a drive crank arm. An upper arm is connected to the drive crank arm and to an upper portion of the nose section so that rotation of the drive crank causes the nose section to move downwardly and rearwardly flexing the skin portion through a desired continuous curvature. A pair of drive links connected to the lower panel and to the upper skin via a bending beam cause additional flexing of the upper skin to achieve the desired curvature.
U.S. Pat. No. 3,994,452 by Cole disclosed a variable camber leading/trailing edge device including a nose structure having an upper flexible panel extending rearwardly from the nose structure and a rib beam connected to the nose structure and which during downward movement pulls the nose downward to bend the upper flexible panel. A 4-bar linkage attached to the nose structure is rotated downward to obtain the desired curvature of the upper panel.
In U.S. Pat. No. 2,755,039--Davie, Jr., there is disclosed a variable camber leading edge including a movable nose portion which is rotated downwardly from the wing to form an increasingly cambered leading edge and a slotted passageway between the rotated nose section and the wing.
Leutholt, U.S. Pat. No. 2,343,986 disclosed a curved nose having an upper portion rotatably mounted on a track for chordwise movement so that the nose is moved upwardly and forwardly against an elastic skin member to effect a change in the camber of the wing.
In U.S. Pat. No. 2,019,819--Jones, there is disclosed an airfoil having an eccentric nose section and several wing sections telescoped along a chordwise axis, so that when the nose section is rotated to increase the size of the leading edge, the wing section is telescoped to extend the chordwise length of the wing in symmetrical ratio to the increase in size of the leading edge.
A co-pending application was filed in the name of the applicant of the present invention on Oct. 9, 1984, Ser. No. 658,674 entitled "Variable Camber Leading Edge Assembly".
Many of the aforementioned variable camber wing assemblies utilize a complex arrangement of levers, arms and gears in an attempt to achieve precise repositioning of the leading edge portion of the wing in order to achieve the desired wing camber. In addition, these variable camber wing assemblies are concerned primarily with the cambering of a leading or trailing edge portion of a fixed wing, rather than with the variable cambering of a slat and/or flap apparatus which is extended and retracted from a wing.